Electronically commutated motor

ABSTRACT

An electronically commutatable motor, whose excitation windings are controllable via semiconductor output stages by an electronic control unit with the aid of PWM control signals, a setpoint value being specifiable to the control unit, and the control unit emitting corresponding PWM control signals to the semiconductor output stages; a motor characteristic curve, from which an assigned nominal operating speed is derivable for the setpoint value being stored in the control unit, and the derived nominal operating speed being able to be compared to the actual speed of the motor. It a predefinable or predefined speed difference between the nominal operating speed and the actual speed is exceeded, the control unit and/or the semiconductor output stages can be switched off. The derivation of the nominal operating speed for the predefined setpoint value is facilitated by a three-dimensional characteristics field determined by four coordinate points.

FIELD OF THE INVENTION

The present invention relates to an electronically commutatable motor, whose excitation windings are controllable via semiconductor output stages by an electronic control unit with the aid of PWM control signals. A setpoint value can be specified to the control unit, and the control unit emits corresponding PWM control signals to the semiconductor output stages. A motor characteristic curve, from which an assigned nominal operating speed is derivable for the setpoint value is stored in the control unit, and the derived nominal operating speed can be compared to the actual speed of the motor. If a predefinable or predefined speed difference between the nominal operating speed and the actual speed is exceeded, the control unit and/or the semiconductor output stages can be switched off.

BACKGROUND INFORMATION

A conventional electronically commutatable motor is described in German Published Patent Application 198 04 874. In that case, the PWM control signals are established in their pulse width by the input of the setpoint value. The comparison of the nominal operating speed, which is assigned to the setpoint value, to the actual speed, is used during the continuous running operation for detecting sharp increases of the setpoint value acting from outside, in order to set the pulse width only gradually to the new value. Since the motor characteristic curve changes as a function of the motor load and the setpoint value, it requires a considerable expenditure of memory in the control unit to ascertain the allocated nominal operating speed.

Storage of the characteristic-curve data of a motor in a memory of the control unit and use of the characteristic-curve data for deriving an operating value is discussed to some extent in the U.S. Pat. No. 5,901,286 and European Published Patent Application No. 0 886 057. In these references, a characteristics field having a plurality of value pairs is used, from which the desired nominal operating value can be derived by interpolation onto a third coordinate. However, this requires a considerable expenditure of memory, particularly when the load of the motor changes.

The object of the present invention is to provide a motor of the type mentioned at the outset with simple data in the control unit, which, with minimal expenditure, for a predefined load, significantly simplifies the derivation of the nominal operating speed corresponding to a predefined setpoint value.

SUMMARY OF THE INVENTION

According to the present invention, this objective is achieved by storing the motor characteristic curve only as a three-dimensional characteristics field having four corner points, which, through coordination with the smallest pulse width and the limiting values of the supply voltage, as well as with the largest pulse width and the limiting values of the supply voltage, are determined by the nominal operating speeds assigned in each case. The nominal operating speed for the comparison to the actual speed is derivable as a function of the existing supply voltage, the predefined setpoint value and the stored coordinate values of the characteristics field.

In this context, advantage is taken of the fact that in many cases, the motor is always loaded with the same consumer, such as in the case of a fan drive. The four coordinate values of the characteristics field take into account not only the pulse widths of the PWM control signals corresponding to the predefinable setpoint values, but also the fluctuations of the supply voltage, and define a characteristics field which allows a clear and simple derivation, i.e. calculation of the assigned nominal operating speed, for the supply voltage present in each case and the control conditions, the connecting lines of the corner points of the characteristics field giving the stipulations for a grid, and thus facilitating the derivation of intermediate values in the coordinate directions for the supply voltage (e.g. x-coordinate) and the pulse widths (e.g. z-direction), and leading to the sought nominal-operating speed (in the y-direction).

Depending upon the use of the motor, according to a further embodiment, the four corner points of the characteristics field may be determined for a predefined motor load. The motor can then be designed in a simple manner for a different load, i.e. consumer.

In this context, according to one refinement of the present invention, the comparison between the nominal operating speed and the actual speed is able to be carried out continually during the continuous running of the motor or repeated at time intervals.

The setpoint value may be specifiable manually in a simple manner using a potentiometer, the control unit being able to be supplied with a variable setting signal which is used for the emission of allocated PWM control signals for the semiconductor output stages. In addition, using this setting signal, the allocated nominal operating speed may be derived on the basis of the stored motor characteristic curve and utilized for the comparison with the actual speed of the motor arising. The actual speed of the motor may be detected in various different ways.

For the comparison of the nominal operating speed and the actual speed, the control unit is coupled to a comparator unit which may be integrated into the control unit.

So that the overload protection does not react to short interference pulses of the actual-speed measurement, one embodiment of the present invention provides for the control unit and/or the semiconductor output stages to be switched off in a time-delayed manner.

If a run-up phase precedes the continuous operation of the motor,-then the overload protection may be designed so that the comparison of the nominal operating speed and the actual speed is first able to be initiated and carried out after a run-up phase of a predefined duration has expired, so that an inadvertent shut-down does not occur during this operating phase. The run-up phase may be preset by the control unit, and the amplitude of the pulses and the pulse width of the PWM control signals, as well as their commutation frequency may be used as parameters. The run-up phase of the motor is able to be initiated with the switch-on of the control unit and/or the semiconductor output stages, and/or the input of a setpoint value for the control unit.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a block diagram of the functional units of an exemplary motor according to an embodiment of the present invention.

FIG. 2 shows a characteristics field stored in the control unit according to an embodiment of the present invention.

DETAILED DESCRIPTION

As the block diagram according to FIG. 1 shows, the motor unit includes an electronic control unit STE which is assigned a comparator unit VE. For a desired continuous operation, a correspondingly adjusted setpoint value N_(setpointv) is specified and provided to this control unit STE. Consequently, after a run-up phase, correspondingly dimensioned PWM control signals pwm are emitted to semiconductor output stages EST which energize the excitation windings of motor M according to the pulse widths of these PWM control signals pwm. An actual speed N_(actual) thereupon sets in at motor M that is detected and supplied as a signal to a comparator unit VE which may be integrated into control unit STE. Control unit STE stores a motor characteristic curve which allows the derivation of a nominal operating speed n_(x) for each setpoint value N_(setpointv). This nominal operating speed n_(x) is obtained more or less exactly in the case of the predefined setpoint value N_(setpointv) if control unit STE, semiconductor output stages EST and motor M are operating correctly, and no conditions exist which lead to a drop in actual speed N_(actual).

Nominal operating speed n_(x), like actual speed N_(actual), is supplied to comparator unit VE, and a speed deviation ΔN is ascertained. If actual speed N_(actual) is more than a predefined or predefinable speed deviation ΔN below expected nominal operating speed n_(x), then a fault exists which can lead to an overload during continuous operation. Therefore, comparator unit VE generates a switch-off signal AB via which control unit STE and/or semiconductor output stages EST can be switched off, as the contacts AB off in the electric circuit of supply voltage U_(batt) indicate.

If setpoint value N_(setpointv) is changed, then PWM control signals pwm, and therefore actual speed N_(actual) of motor M change, as well. A correspondingly new nominal operating speed n_(x) is supplied to comparator unit VE, and the comparison is carried out in the same manner for the new continuous operation with altered speed.

The switch-off of control unit STE and/or of semiconductor output stages EST may also be initiated in a delayed fashion, in order to suppress spurious peaks in the derived and detected speed values.

Permissible speed deviation ΔN may also be made a function of the magnitude of predefined setpoint value N_(setpointv) and the existing magnitude of supply voltage u_(x). The comparison by comparator unit VE may be carried out continually during the continuous operation, or repeated at time intervals. In addition, the overload protection by the comparison and the shutdown may first be switched to effective after reaching the nominal operating speed specified by the setpoint value, i.e. after a predefined or predefinable run-up time has expired. In this context, the run-up time may be started with the switching-on, that is to say, with the feeding of supply voltage u_(x) to control circuit STE and/or to semiconductor output stages EST, and/or with the application of a predefined setpoint value N_(setpointv) to control unit STE.

Nominal operating speed n_(x), derived and calculated by control unit STE, is a function not only of existing supply voltage u_(x) with its limiting values u₁ and u₂, but also of stored speeds n₁₁, n₁₂, n₂₁, n₂₂ of the corner points of characteristics field KF, as the specification n_(x)=f (N_(setpointv), u₁, u₂, n₁₁, n₁₂, n₂₁, n₂₂) in the Figure indicates, and as is clarified later.

As the three-dimensional characteristics field KF according to FIG. 2 shows, the voltage range from U_(max) to U_(min) is plotted in the x-direction, while the pulse width from pwm_(min) to pwm_(max) extends in the z-direction. In the exemplary embodiment, U_(max)=13V and U_(min)=8V are selected, and the pulse width has a range from pwm_(min)=60% to pwm_(max)=100%. For the smallest supply voltage, given pwm_(min)=60% and pwm_(max)=100%, nominal operating speeds of n₁₁=50 min⁻¹ and n₂₁=1800 mm⁻¹ result, while for the greatest supply voltage, given pwm_(min)=60% and pwm_(max)=100%, nominal operating speeds n₁₂=150 min⁻¹ and n₂₂=2900 min⁻¹ result. These nominal operating speeds n₁₁ to n₂₂ define the four corner points P1 to P4 in three-dimensional characteristics field KF. The connecting lines between corner points n₁₁ and n₂₁, n₁₁ and n₁₂, n₂₁ and n₂₂, and n₁₂ and n₂₂, respectively, permit the formation of a grid which, for existing supply voltages U_(x) and pulse width pwm_(x) corresponds to a setpoint value. Formation of the grid allows the derivation of allocated nominal operating speeds n_(x) on straight line n1 _(x)-n2 _(x). Thus, given a supply voltage of U_(x)=10.5V and a pulse width of approximately 87%, a nominal operating speed of approximately 1800 min⁻¹ can be interpolated from characteristics field KF.

This characteristics field KF is valid for a specific motor for a predefined, constant load. For a further load, a characteristics field KF valid for the further load can be stored in control unit STE.

As the three-dimensional characteristics field KF according to FIG. 2 shows, supply voltage u_(x) having the voltage range from smallest supply voltage u₁=8V to greatest supply voltage u₂=13V is plotted in the x-direction. In the z-direction, pulse width pwm of the PWM control signals is predefined, which may extend from minimal pulse width pwm₁=60% to maximum pulse width pwm₂=100%. Given a preselected load of the motor, four limit operation cases are ascertained with u₁ and pwm₁, u₁ and pwm₂, u₂ and pwm₁, as well as u₂ and pwm₂, which lead to nominal operating speeds n_(x)=n₁, n₁₂, n₂₁ and n₂₂, and consequently define characteristics field KF according to FIG. 2.

If motor M is loaded with a different load, then a similar characteristics field KF results having new nominal operating speeds n₁₁, n₁₂, n₂₁ and n₂₂.

The following values result for characteristics field KF of an exemplary embodiment shown in FIG. 2:

n₁₁=50 min⁻¹ at u₁=8V and pwm₁=60%

n₁₂=150 min⁻¹ at u₂=13V and pwm₁=60%

n₂₁=1800 min⁻¹ at u₁=8V and pwm₂=100%

n₂₂=2900 min⁻¹ at u₂=13V and pwm₂=100%

Characteristics field KF can be represented as a grid, the connecting lines between corner points n₁₁ and n₁₂, and n₂₁ and n₂₂, respectively, as well as n₁₁ and n₂₂, and n₁₂ and n₂₂, respectively, specifying the gridding, and as is shown, for an existing supply voltage u_(x), permitting the derivation of allocated nominal operating speed n_(x) in the case of existing PWM control signal p_(x). PWM control signal pwm_(x) is allocated to predefined setpoint value N_(setpointv).

As grid line nx₁-nx₂ shows, in the case of u_(x)=10.5V and a pulse width of pwm_(x)≈87.5%, the derivation of nominal operating speed n_(x) leads to a value of approximately 1800 min⁻¹.

To calculate nominal operating speed n_(x) allocated to a setpoint value N_(setpointv), one proceeds as follows with interpolated coefficients stg1, stg2 and stg3: ${stg1} = {{\frac{n_{12} - n_{11}}{u_{2} - u_{1}}\quad {stg2}} = \frac{n_{22} - n_{21}}{u_{2} - u_{1}}}$ n_(1x) = n₁₁ + stg₁ * (u_(x) − u₁) n_(2x) = n₂₁ + stg₂ * (u_(x) − u₁) ${stg}_{3} = {\frac{n_{2x} - n_{1x}}{{pwm}_{2} - {pwm}_{1}} = \frac{n_{21} - n_{11} + {\left( {{stg}_{2} - {stg}_{1}} \right)*\left( {u_{x} - u_{1}} \right)}}{{pwm}_{2} - {pwm}_{1}}}$

Thus, n_(x) = n_(1x) + stg₃ * (pwm_(x) − pwm₁)

Since the calculations use the reciprocal of the speed values, the above equation for calculating surface point n_(x) must be changed around accordingly. With T_(x)=a/n_(x), it follows that: $\frac{a}{T_{x}} = {n_{1x} + {{stg}_{3}*\left( {{pwm}_{x} - {pwm}_{1}} \right)}}$ $T_{x} = \frac{a*\left( {{pwm}_{1} - {pwm}_{2}} \right)}{\left( {{\left( {{\left( {{stg}_{1} - {stg}_{2}} \right)*u_{x}} - n_{21} + n_{11} + {\left( {{stg}_{2} - {stg}_{1}} \right)*u_{1}}} \right)*{pwm}_{x}} + {\left( {{{pwm}_{1}*{stg}_{2}} - {{pwm}_{2}*{stg}_{1}}} \right)*u_{x}} + {{pwm}_{1}*\left( {n_{21} - {u_{1}*{stg}_{2}}} \right)} + {{pwm}_{2}*\left( {{stg}_{1}*u} \right.}} \right.}$

In the formula above, only supply voltage U_(x) and the pulse width of output-stage control pwm_(x) are variable. The remaining factors may be stored as fixed parameters in the ROM or EEPROM. Following is once again the same formula with the variable names used in the program code. ${v\_ tx} = \frac{{K\_ ZAEHL}_{1}}{\left( {{\left( {{K\_ NENN}_{1} + {v\_ ubat} + {K\_ NENN}_{2}} \right)*{v\_ pwm}{\_ endst}} + {{K\_ NENN}_{3}*{v\_ ubat}} + {K\_ NENN}_{4}} \right)}$

During the programming at the rear end of the assembly line, the corresponding parameters can now be transferred from the test stand into the EEPROM of the motor control.

Wherein:

K_NENN₁=(stg₁−stg₂)

K_NENN₂=(−n₂₁+n₁₁+(stg₂−stg₁)*u₁

K_NNEN₃=(pwn₁*stg₂−pwm₂* stg₁)

K_NENN₄=pwm₁*(n₂₁−u₁*stg₂)+pwm₂*(stg₁*u₁−n₁₁)

K_ZAEHL₁=a*(pwm₁−pwm₂)

v_ubat=u_(x)

v_pwm endst=pwm_(x). 

What is claimed is:
 1. An electronically commutatable motor having excitation windings, comprising: at least one semiconductor output stage; an electronic control unit controlling the excitation windings via the at least one semiconductor output stage by emitting control signals corresponding to an adjustable control signal and a setpoint value, the electronic control unit further storing a motor characteristic curve from which an assigned nominal operating speed is derivable for the setpoint value, the derived nominal operating speed being comparable to an actual speed of the motor; wherein, if a predefined speed difference between the nominal operating speed and the actual speed is exceeded, at least one of the electronic control unit and the at least one semiconductor output stage can be switched off, and wherein the motor characteristic curve is stored as a characteristics field having four three-dimensional corner points, each representing operating speeds of a characteristics field for a predefined, constant load, the corner points being determined by limiting values of a supply voltage and limiting values of the control signals, lines connecting the four corner points of the characteristics field permitting formation of a grid, from which, for an existing supply voltage and a control signal corresponding to the predefined setpoint value, the nominal operating speed is derivable from comparison to the measured actual speed.
 2. The electronically commnutatable motor of claim 1, wherein comparison between the nominal operating speed and the actual speed is carried in one of the following ways: i) continually during a continuous operation of the motor; and ii) repeated at time intervals.
 3. The electronically commutatable motor of claim 1, wherein the setpoint value is manually adjusted using a potentiometer.
 4. The electronically commutatable motor of claim 1, wherein, for comparison of the nominal operating speed and the actual speed, the electronic control unit is coupled to a comparator unit.
 5. The electronically commutatable motor of claim 1, wherein the comparator unit is integrated into the electronic control unit.
 6. The electronically commutatable motor of claim 1, wherein the switching off of the at least one of the electronic control unit and the at least one semiconductor output stage is carried out in a time-delayed manner.
 7. The electronically commutatable motor of claim 1, wherein comparison of the nominal operating speed and the actual speed is initiated and carried out only after a ran-up phase of a predefined duration has expired.
 8. The electronically commutatable motor of claim 7, wherein the run-up phase can be initiated with a switching-on of at least one of the electronic control unit, the at least one semiconductor output stage, and the input of a setpoint value. 